The invention relates to an actuating means able to be activated by fluid power, comprising a hose body extending between two spaced head pieces and whose interior space is able to be subjected to a fluid medium, and a strand structure fixed to both head pieces and extending coaxially in relation to the hose body, such strand structure being composed of two strand groups in a crossover configuration with bendingly flexible strands extending adjacent to one another with the same longitudinal alignment within a strand group.
An actuating means of this type is disclosed in the European patent publication 0 161 0750 B1. In this known design the hose body consisting of bendingly flexible material is externally surrounded by strand structure consisting of fiber material, which is made up of two strand groups, which assume a crossover configuration in relation to one another. In this case the strand groups are plaited together so that there is a knot-free cross linking effect. Under the action of pressure in its interior space the hose body expands radially, something which owing to cooperation with the strand structure leads to a reduction of the distance between the two head pieces. One problem with the known actuating means is the high friction occurring in the crossover region of the individual strands during a change in diameter of the hose body. This is more particularly caused by changes in angle between the strands of the two strand group. In the case of the said European patent publication 0 161 0750 B1 there is consequently a suggestion to apply a lubricant to the points of intersection of the strands of the individual strand groups. Apart from the work of applying such lubricant there is however also the chance of lubricant evaporating in the course of time or, in the case of the lubricant being a solid coating, gradually being scraped off so that the lubricating effect will decrease as time goes by and friction-dependent damage may occur on the strand structure.
Accordingly one object of the present invention is to create an actuating means of this type whose strand structure is hardly subject to wear even in the case of prolonged periods of operation.
In order to achieve this object there is the provision such that an intermediately placed yielding material between the strand groups serves to maintain the stand groups constantly at a distance apart.
It is in this manner that direct contact between the two strand groups is prevented. The necessary distance apart is ensured by a material placed between the strand groups, which practically assumes the function of a partition wall, but which however owing to its yielding properties does not disadvantageously influence the freedom to move of the strands. Owing to the avoidance of direct contact between the strand groups the load on the strand material is substantially reduced and simultaneously the efficiency of the actuating means is improved.
Advantageous further developments of the invention will appear from the dependent claims.
The strand groups are preferably embedded in a flexible and more particularly rubber elastic material, the strand groups being preferably completely surrounded by this material, this meaning at the same time a protection against external effects.
It would in principle be possible to manufacture the strand structure separately from the hose body and to place it as a sort of concentric casing around the hose body. However it is substantially simpler and cheaper to have a design in the case of which the material holding the strand groups at the distance apart is directly constituted by the hose body, that is to say the strand structure is integrated in the material of the hose body, which thus, in addition to its sealing function for the interior space receiving the fluid under pressure, simultaneously assumes the spacing function for the strand groups. It would be feasible as well for instance for the material of the hose body material to be held in a suitable manner in the peripheral portion of the strand groups by vulcanization.
It is furthermore an advantage for the strands to extend within the individual groups thereof without making contact with one another, the material holding the strand groups apart simultaneously being able to serve as a means preventing contact between the strands within the individual groups.
In the case of a particularly convenient design there is a provision such that the strand groups are not cross linked with each other and surround one another coaxially. This renders possible, on the one hand, an extremely simple laying of the strands without complex plaiting. On the other hand the two strand groups run in two mutually concentric tubular layers, which do not penetrate one another radially so that the individual strands have a wave-free form which is stretched out in their principal direction, this meaning a reduction in loads on the material and an improvement in the response characteristic.
In the following the invention will be described in detail with reference to the drawings.